I am new in raspberry pi.
In my research project, I would like to monitor ground temperature at 60 points. My team decided to set a monitoring system using raspberry pi. 

As a preliminary test, I connected 4 DS18B20 sensors to my pi; it can find sensors and read temperature correctly. Unfortunately, when I connected an additional DS18B20 to the pi (so total 5 DS18B20 were linked to the pi), it stopped monitoring and gave no value. (I tried to reboot the system; however the pi can't read the temperature)

After this weird situation, I disconnected the last sensor (so subsequently total 4 sensors were connected to the pi); then the pi started to read the temperature.

I really want someone can explain this to me.

Thank you for reading.